1. Field of the Invention
This invention relates to a display device, especially to a technology for reducing display device size by improving layout flexibility of peripheral driving circuits.
2. Description of the Related Art
A flat panel display device including a reflection type active matrix liquid crystal display device (referred to as LCD hereinafter) can be thin, small and light, and it operates with low-power consumption. The LCD has been used as a display part in various devices such as mobile information device. The LCD, whose pixel has a switching element and a thin film transistor, is known as an active matrix type. The panel of the active matrix display device is highly reliable for maintaining displayed contents of the pixels, which provides the active matrix display device with high display quality.
FIG. 3 shows an equivalent circuit of a pixel in the active matrix LCD. Each pixel has a thin film transistor (TFT) 11 connected to a gate line and a data line. When the TFT 11 is turned on by a selection signal outputted to the gate line, the data corresponding to the display content is supplied to a liquid crystal capacitance (Clc) 15 from the data line through the TFT 11. It is necessary to accurately keep the display data from the time when the TFT 11 is first selected for writing to the time when the TFT 11 is selected again in the next sequence. Therefore, a storage capacitance (Csc) 13 is connected to the TFT 11 in series with the liquid crystal capacitance Clc 15.
FIG. 4 is a plan view showing the configuration of a LCD panel 300 as a whole. A display region 100 is disposed in the middle of the LCD panel 300. The display pixels are disposed in a matrix configuration on the display region 100. And peripheral driving circuits including an H scanner (a horizontal driving circuit) 101, a HSW circuit 102, a PSW circuit 103, a V scanner (a vertical driving circuit) 104 and a group of input terminals 105 are disposed near the inside wall of the display region 100.
The H scanner 101 generates a horizontal scanning signal. The HSW circuit 102 is a switching circuit for supplying a video signal to the data line based on the horizontal scanning signal. The PSW circuit 103 is a switching circuit, which is connected to all the data lines and turns them on and off simultaneously. When the PSW circuit 103 is on, it supplies a pre-charge data (pre-charge signal) from a pre-charge bus line to all the data lines.
The V scanner 104 is a circuit for outputting a vertical scanning signal, which becomes high for each of the horizontal period, as the selection signal described above is applied to the gate line.
An HVDD (a source voltage for the H scanner), a VSS (an earth voltage), the pre-charge data, a VVDD (a source voltage for the V scanner) and a VCOM (a common voltage) are inputted from the group of input terminals 105, and an HVDD bus line 110, a VSS bus line 111, the pre-charge data bus line 112, a VVDD bus line 113, and a COM bus line 114 corresponding to the above mentioned voltages are disposed around the display region 100. These bus lines 110-114 supply the data and the voltages necessary for peripheral driving circuits.
However, since various bus lines 110-114 are formed as a part of the wiring layer that is made of poly-silicon or an aluminum and is also used for the peripheral driving circuit, there is a certain restriction in terms of the circuit layout. Additionally, it is necessary to reduce the time constant of these bus lines 110-114. Therefore, for a larger LCD panel, a wider wiring area is required, enlarging the framing area of the LCD panel 300.
The invention provides a display device having a plurality of wiring layers. The display device includes a display region having a plurality of display pixels and a peripheral driving circuit that supplies a driving signal to each of the display pixels and is disposed outside the display region. The display device also includes a bus line that supplies a voltage to the peripheral driving circuit and a pixel electrode disposed for each of the display pixels. The bus line and the pixel electrodes are disposed in one of the wiring layers, and at least a portion of the peripheral driving circuit is disposed in a wiring layer that is disposed below the wiring layer of the bus line and the pixel electrodes.
The invention also provides a reflection-type display device having a plurality of wiring layers. The display device includes a display region having a plurality of display pixels and a peripheral driving circuit that supplies a driving signal to each of the display pixels and is disposed outside the display region. The display device also includes a bus line that supplies a voltage to the peripheral driving circuit and a reflection pixel electrode disposed for each of the display pixels. A wiring layer of the reflection pixel electrode includes a portion of the peripheral driving circuit or a portion of the bus line.